Watt-hour power meters have been known in the art of electric power conduction for many years. In a typical embodiment, a building such a commercial establishment has incoming current from a utility power network. This current passes through a meter socket adapted to attach a watt-hour meter to the circuit for measuring and billing power consumption. The power line from the utility power grid is connected to the line end of the meter socket, and the building receives the appropriate amount of power through the load end of the meter socket.
Numerous pieces of equipment have been used to conveniently and safely attach the watt-hour meter to the circuit being measured. The circuit may incorporate sockets that are rated according to the maximum current that is allowed to flow through the socket, which depends upon the electricity needs of the building at hand. Accordingly, numerous watt-hour meters are available to fit the various meter sockets that are appropriate for different operating conditions. In fact, Landis and Gyr, one manufacturer of meters and meter socket equipment, makes its Meter Socket Application Guide available on the Internet for convenient use (www.lanisandgyr.com). This guide notes that certain installations use either self-contained meter sockets or transformer rated sockets, depending upon the service type at hand.
A self-contained meter socket allows the user to connect the meter directly to the meter socket—in the absence of additional, external current transformers proximate the socket. In most situations, current transformers are housed in the meter itself for self-contained installations. In a different scenario, a current transformer rated meter socket, also known as a CT-rated socket, pulls current from the utility company's power network grid through a series of specially calibrated current transformers. The current transformers, often housed in a cabinet directly adjacent the meter socket, bring the current level from the utility power grid down to an appropriate level for the building to use. A proper kind of meter attaches to the meter socket after the current has been transformed to an appropriate level. For example, a 600 amp current may be transformed to 5 amps in a current transformer enclosure before entering the CT-rated socket to meet governmental codes and industry specifications.
As noted in the Landis and Gyr Meter Socket Application Guide, electrical service may be, for example, single phase, 3-phase/3-wire, and 3-phase/4-wire in either a wye or delta wiring arrangement. Each of these set-ups require a planned approach to the form of meter (e.g., 2 S, 3 S, 5 S, 14K, and the like) and the socket type that describes the number of jaw contacts and the current rating (e.g., K-7 480 A continuous/600 A Maximum current rating). These designations are well-known in the art of power metering.
One type of self-contained metering installation that has become prevalent in recent years is K-Base metering. See prior art FIG. 2 herein. K-Base metering utilizes a meter socket that is equipped to handle continuous electric loads greater than 320 amperes using self-contained meters attached directly to the meter socket (e.g., bolted thereon). K-Base metering has proven useful in class 400 ampere continuous duty as well as for applications seeing intermittent loads up to 600 amps.
The rugged construction and the thick current connectors allow K-Base meter socket connections to significant current loads. The watt-hour meter used on a K-Base meter socket is bolted onto the respective line and load socket connectors. When a facility uses high currents (i.e., above 320 amperes) consistently, it is also permissible for current transformer boxes to be added to an installation to bring currents down to more useful levels before transmitting current to a K-Base meter. It simply depends upon the needs of the installation. Of course, adding current transformer boxes adds to the cost and space requirements of the installation.
In any power metering installation, bolting and un-bolting the meter presents a significant danger to the person working on the site. In certain embodiments, the meter socket carries dangerous current levels that are transformed within the meter itself. When a consumer or utility worker removes the meter, the full current load on the socket is exposed. Accordingly, personnel who work on or near that meter socket face grave consequences if they touch a live socket by accident.
Numerous devices have been used to make watt-hour meter installations safer and more convenient, especially for high currents up to 600 amperes. Prior efforts to address high current level power meter installations include transforming the current with known coil-type current transformers that significantly lower the current level actually measured by the meter. The transformed current, of course, can be measured and then proportionally converted by metering software to accurately determine the power consumption on the original line. Unfortunately, efforts to utilize this technology have required rewiring an existing circuit to install the transformers and then run the transformed current leads to a separate location for metering. This is quite a bit of work and still requires a technician to deal directly with the high current lines. See U.S. Pat. No. 7,232,335 (Preuhs 2007).
The Preuhs '335 patent also discloses a watt-hour meter adapter with current transformers about its bus bars that run through the adapter housing. Current leads from the current transformers are directed to jaw contacts on the housing which ultimately engage a watt-hour meter. The problem with the Preuhs design, as shown in FIG. 17 therein, is that the current transformers are installed in the same housing that connects the meter jaw contacts. In this embodiment, the high current bus bars are directly adjacent the upper face of the jaw contact housing and are in close proximity to the areas manually handled by power technicians. The Preuhs embodiment, therefore, is not safe for currents on the bus bars up to 600 amperes. In fact Preuhs limits its use to CT-rated meters (col. 9, lines 10-47).
Other adapters have been developed for various K-Base metering applications, but these have required large current transformers that do not easily fit within the meter socket without inconveniently shaped housings for the adapter. Other adapters simply do not include transformers within the adapter itself and rely on outside current transformer enclosures to bring the currents down to measurable levels.
A need continues to exist in the art of watt-hour metering for a meter socket adapter that fits properly into a meter socket, allows for a wider variety of watt hour meters to be installed in the socket, allows fast and safe installation and removal of the watt-hour meter by technicians, and properly insulates the exposed face of the adapter from high currents on the meter socket.